The invention relates to a circuit arrangement for controlling the speed of rotation of a hydrostatic machine, in particular a secondary-controlled machine connected to a pressure line and having the features set forth in the preamble of claim 1.
If the speed control of the machine is carried out electrically, an electronic speed controller is supplied with the speed desired value and the speed actual value of the hydrostatic machine generated in a tachogenerator or other pickup. Connected to the speed controller is a pivot angle adjustment. The pivot angle of the hydrostatic machine operating as motor for driving a load defines the absorption volume. As long as the working pressure supplied to the machine is constant, the torque of the engine is proportional to the pivot angle. The adjustment can be made with the aid of a control magnet and hydraulic valve with mechanical feedback or also with a servo value and electrical feedback.
If the load is to be accelerated in the speed controller, an output signal (manipulated variable) is generated which increases the pivot angle of the motor and thus the motor torque. The instantaneous difference between the load torque, the motor losses and the motor torque is available as acceleration moment for the drive. The acceleration and thus the speed increase of the load depends on the torque difference and the mass to be accelerated in such a manner that with a maximum pivot angle of the motor arising on corresponding presetting of the speed desired value and with a small load moment and small mass maximum acceleration of the drive is obtained. In such cases the speed increase of the drive takes place too rapidly. Since the adjusting time for adjusting the pivot angle of the motor cannot be shortened to any desired extent, the drive reaches a speed far above the desired speed by the time the pivot angle of the motor can be reduced. Thus, a pronounced overshooting of the speed results in a long settling time until the desired speed is reached.
From this derives the problem underlying the invention of improving the control behaviour of the hydrostatic machine and limiting the settling time in such a manner that the drive is accelerated in dependence upon the load so that the speed fluctuations outlined are avoided.